Calcium supplements—previously thought to help prevent heart disease and stroke—have now been shown to almost double the risk of heart attack. Doctors are now warning that such supplements should be taken with caution, and even then only for vital medical reasons.

The new finding is based on a large-scale study of 23,980 men and women in Heidelberg, Germany. The participants were part of a cancer and nutrition study, but the results also allowed researchers to assess how calcium supplements were linked to heart disease.

The team of researchers, from Zurich University's institute of social and preventative medicine, found that people who used calcium supplements regularly were 86 percent more likely to suffer a heart attack than those who did not. Those who obtained their calcium just from supplements were 2.7 times more likely than non-users to experience a heart attack. The results are published in the journal Heart.

While calcium is required for bone growth, it is also used by other organs such as the heart. While there is clear evidence that some calcium supplements should be taken to protect bones—in certain medical situations—this new research points to the fact that such action should be taken only under close consultation with a doctor. Dr Claire Bowring, of the UK's National Osteoporosis Society, explained to the Guardian:

"This study further highlights the need for care when considering taking calcium supplements. If you get all of the calcium that you need from your diet then a supplement will not be necessary. Boosting calcium beyond recommended levels has no extra benefit for bones.

"Supplementation may be warranted if you are unable to get enough calcium in your diet, but it needs to be done with consideration."

The message is clear that patients should consult a physician before taking calcium supplements—especially if they are at risk of a heart disease or heart attack. [Heart via The Guardian]